The purpose of a sputter gun is to dislodge particles of material, such as metal, from a target and direct those particles to a substrate whereat they adhere to form a film on the substrate. Such sputtering takes place in a vacuum chamber. In the prior art, ionizable gas has been added to the vacuum chamber and a magnetron, which provides EXB forces, causes the gas to ionize and become a dense and localized plasma. The term ionizable gas means gas which is intended to ionized and throughout this description the term "gas" includes vapors as well. Within the plasma, mentioned above, there are electrons, ions and electronic neutrals. The ions, which are positively charged, are attracted to a cathode device which is the target. Those ions bombard the target, dislodge particles of cathode material and a large number of such particles, which are dislodged, leave the target and travel to the substrate. In some prior art arrangements, the substrates are located so as to be in the path position of the particle excursions. In the prior art the ionizable gas in the vacuum chamber, prior to ionization, is at least greater than two millitorr and generally of the order of ten millitorr. These relatively high gas pressures have been necessary heretofore to secure sufficient ionizing collisions to sustain the magnetron discharge. However such relatively high pressure gases cause problems for the sputtering technique. For instance, the gas molecules in the vacuum chamber moving about between the substrate and the target deflect the dislodged particles away from the substrate and this gives rise to low deposition efficiency. In addition, in the prior art, the large number of gas molecules present in the vacuum chamber results in many of them becoming occluded in the growing film. The contamination of the sputtered film by gas molecules produces a film which is less pure and which is porous. The density of the gas between the target and the substrate represents an impediment to the particles leaving the target. Accordingly the substrate must be located close to the target, in the prior art, so that a dislodged particle does not dissipate its energy colliding with gas molecules while traveling toward the substrate, thus impairing adhesion. The present device, because it provides pre-ionized gas to the magnetron chamber, enables the generation of plasma by the magnetron at a considerably lower gas pressure than is possible without pre-ionization.